Recently electric vehicles (electrically-driven vehicles), which deliver less environmental burden than conventional vehicles using fossil fuel, are under development. If the electric vehicle is required to perform the same performance as the conventional vehicle, a high-cost secondary battery need be used and hence the secondary battery impedes wide application of electric vehicles.
It is proposed to provide a system, which promotes electric vehicles by effectively using a secondary battery of an electric vehicle as an electric power source for home use (for example, JP-A-2002-315193).
This system includes a switching device, which connects either one of a commercial AC power supply system and a secondary battery to an electric load at a home and disconnects the other and the home electric load. The switching device performs either one of first and second switching states. In the first switching state, the electric power is supplied from the AC power supply system to the home load. In the second switching state, the electric power is supplied from the secondary battery to the home load.
A switching device may be formed as a comparative embodiment, which has as shown in FIG. 19 a switch 10A and a switch 10B. The switch 10A is a power supply system side switch provided between a commercial AC power supply system 4 and an electric load 3 at a home. The switch 10B is a secondary battery side switch provided between an electric vehicle 2, on which a DC secondary battery 2a and a DC-AC conversion unit 2b are mounted, and the load 3.
For example, in a case that the power supply is switched from the first switching state, in which the load 3 is connected to the AC power supply system, to the second switching state, in which the load 3 is connected to the secondary battery 2a side, it is necessary to turn on the switch 10B after turning off the switch 10A so that the AC power supply system side and the secondary battery 2a side are not connected to the load 3 at the same time. If the switches 10A and 10B are formed of electromagnetic switches, respectively, the switches 10A and 10B need long time to perform the switching from the first switching state to the second switching state. This switching time is likely to cause a temporary shut-down of electric power to the home load. If the switches 10A and 10B are formed of semiconductor switches such as triacs, respectively, the switching time may be shortened. However, a leak current flows continuously under a state that the switch 10A is in the off-state. As a result, the AC power supply system and the load 3 are half-connected to each other.